import sys
import math

def distance(x1, y1, x2, y2):
	return math.sqrt((x1 - x2)**2 + (y1 - y2)**2)	

#fin = open("test.txt", "r")
fin = sys.stdin

[x1, y1, x2, y2] = list(map(float, fin.readline().split()))

print("{0:.5f}".format(distance(x1, y1, x2, y2))) import sys sys import math math def distance(x1, y1, x2, y2):
	return math.sqrt((x1 - x2)**2 + (y1 - y2)**2)	

#fin = open("test.txt", "r") distance return math.sqrt((x1 - x2)**2 + (y1 - y2)**2) math.sqrt((x1 - x2)**2 + (y1 - y2)**2) math.sqrt math sqrt (x1 - x2)**2 + (y1 - y2)**2 (x1 - x2)**2 x1 - x2 x1 x2 2 (y1 - y2)**2 y1 - y2 y1 y2 2 x1 x1 y1 y1 x2 x2 y2 y2 fin = sys.stdin fin sys.stdin sys stdin [x1, y1, x2, y2] = list(map(float, fin.readline().split())) [x1, y1, x2, y2] x1 y1 x2 y2 list(map(float, fin.readline().split())) list map(float, fin.readline().split()) map float fin.readline().split() fin.readline().split fin.readline() fin.readline fin readline split print("{0:.5f}".format(distance(x1, y1, x2, y2))) print "{0:.5f}".format(distance(x1, y1, x2, y2)) "{0:.5f}".format "{0:.5f}" format distance(x1, y1, x2, y2) distance x1 y1 x2 y2 fin = sys.stdin sys.stdin fin def distance(x1, y1, x2, y2):
	return math.sqrt((x1 - x2)**2 + (y1 - y2)**2)	

#fin = open("test.txt", "r") def distance(x1, y1, x2, y2):
	return math.sqrt((x1 - x2)**2 + (y1 - y2)**2)	

#fin = open("test.txt", "r") distance
import sys
import math

def distance(x1, y1, x2, y2):
	return math.sqrt((x1 - x2)**2 + (y1 - y2)**2)	

#fin = open("test.txt", "r")
fin = sys.stdin

[x1, y1, x2, y2] = list(map(float, fin.readline().split()))

print("{0:.5f}".format(distance(x1, y1, x2, y2)))